DESCRIPTION, EXTERNAL MORPHOLOGY, AND NATURAL HISTORY OBSERVATIONS OF NEBALIA HESSLERI, NEW

SPECIES (PHYLLOCARIDA: LEPTOSTRACA), FROM SOUTHERN CALIFORNIA, WITH A KEY TO THE EXTANT

FAMILIES AND GENERA OF THE LEPTOSTRACA

JOEL W. MARTIN, ERIC W. VETTER, AND CORA E. CASH-CLARK

Made in United States of America Reprinted from JOURNAL OF CRUSTACEAN BIOLOGY

Vol. 16, No. 2, May 1996 Copyright 1996 by The Crustacean Society

JOURNAL OF CRUSTACEAN BIOLOGY, 16(2): 347-372, 1996

DESCRIPTION, EXTERNAL MORPHOLOGY, AND NATURAL HISTORY OBSERVATIONS O F NEBALIA HESSLERI, NEW

SPECIES (PHYLLOCARIDA: LEPTOSTRACA), FROM SOUTHERN CALIFORNIA, WITH A KEY TO THE EXTANT

FAMILIES AND GENERA OF THE LEPTOSTRACA

Joel W. Martin, Eric W. Vetter, and Cora E. Cash-Clark

A B S T R A C T A new and relatively large species of leptostracan crustacean, Nebalia hessleri, is described

from enriched sediments and detrital mats off southern California. The new species is charac­terized by its size, possession of "normal" (versus lobed) eyes, rectangular and unpaired sub-rostral keel, acute dentition of the posterior pleonite borders, and caudal furca approximately twice the length of the telson. Clark's Nebalia pugettensis (Clark, 1932) is herein declared a nomen nudum. The new species differs from specimens at Friday Harbor, Puget Sound, Wash­ington, in the form of the epimeron of the fourth pleonite, the dentition along the posterior border of the fifth through seventh pleonites, the relative length of the telson and caudal furca, and size. Coloration may also serve to distinguish N. hessleri from other species if egg-bearing females are available; eggs of N. hessleri are cream or gold colored. The new species differs from a currently unnamed sympatric species that occurs in adjacent sand flats (Vetter, in press) primarily in the morphology of the first antenna, which is greatly reduced in the sand-flat species, and the eye, which has unique dorsal and ventral corneal protrusions in the sand-flat species.

Selected aspects of the external morphology of the new species are illustrated via scanning electron microscopy, highlighting a previously unappreciated diversity of spines and setal types. Based on these photographs, some limbs are suggested as having sensory functions. Selected features of the Friday Harbor specimens also are illustrated via SEM. Limited notes on feeding behavior and oxygen level tolerances are provided, based on preliminary laboratory observa­tions. Finally, we include a morphology-based key to identification of the currently recognized families and genera of the Leptostraca.

The phyllocarid crustacean order Lepto­straca is currently recognized as comprising two extant families: Nebaliopsidae Hessler, 1984, containing only the genus Nebaliop-sis G. O. Sars, 1887, and Nebaliidae Baird, 1850 (emended by Hessler, 1984), contain­ing the genera Nebalia Leach, 1814, Par-anebalia Claus, 1880, Nebaliella Thiele, 1904, Dahlella Hessler, 1984, Sarsinebalia Dahl, 1985, and Speonebalia Bowman, Ya­ger, and Iliffe, 1985 (see Hessler, 1984; Dahl, 1985; Bowman et al, 1985). In Cal­ifornia waters, only the genus Nebalia has been reported, and it has been assumed un­til recently that all specimens belong to a single species, Nebalia pugettensis (Clark, 1932) (originally described as Epinebalia pugettensis, transferred to Nebalia by Can­non, 1960). Because of similarities between Clark's description of N. pugettensis and the species described in this paper, it may be necessary to revive Clark's original ge­

nus, Epinebalia, at some later date (see Dis­cussion).

Recent and ongoing ecological work in the area of La Jolla, San Diego, California, by one of us (EWV) (Vetter, 1994, 1995, and in press) has demonstrated that there are at least four leptostracan species found along the coast of western North America, only one of which {N. pugettensis) has been previously described (and that one incom­pletely so), with the description of a second species currently in press (Vetter, in press). In this study, we declare the sole previously described west coast species, N. pugettensis (Clark, 1932), to be a nomen nudum, and describe a new species from detrital mats in submarine canyons off the coast of southern California. The average number of individ­uals in these mats has been estimated to reach 1.5 million/m^, contributing to the highest density of any macrofaunal assem­blage yet reported (Vetter, 1994; see below and Vetter, 1995, for more detailed habitat

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notes). In addition, we extend what little is known about leptostracan ultrastructural morphology by describing selected mor­phological features using scanning electron microscopy; compare some of these fea­tures to those of specimens collected near Friday Harbor, Washington (the original collecting site of A', pugettensis); provide preliminary observations on the natural his­tory (feeding and oxygen level tolerances) of the new species; and provide a key to the extant families and genera of the Lep-tostraca.

MATERIALS AND METHODS

Animals were collected during ecological investi­gations of the benthic community off the coast of l-a Jolla, California, U.S.A. The habitat consists of detrital mats with low oxygen levels (see Vetter, 1995) in sub­marine canyons. The habitat is dynamic, with the de­trital mats expanding during summer periods of calm and contracting when surge, generated by winter storms, moves some or all of the material deeper into the canyon. The mats are composed primarily of surf grass (Phyllospadix spp.) and kelp (Macrocystis pyri-fera (Linnaeus, 1771), Egregia menziesii (Turner, 1808), Laminaria spp., Pterygophora californica Ru-precht, 1852), though other algae including Sargassum spp., Ulva sp., Pelvelia fastigiata Setchell and Gardner, 1917, and a variety of small red algae are sometimes common. Collections from which the specimens de­scribed herein were taken were made on 29 February 1992 using an air-powered suction device on a detrital mat at the head of Scripps Canyon, approximately 1,000 m north of the Scripps Institution of Oceanog­raphy pier, at approximately 32°52.5'N, 117°15.5'W, at a depth of 60 feet (19 m).

The detrital mats were sampled at least monthly, as weather permitted. Cores were taken using a large steel cylinder (0.185 m-'), which was used to isolate a por­tion of the mat. Hedge trimmers (shears) were used to cut the detritus along the inner wall of the cylinder, and then a vacuum lift was used to remove the material from within the cylinder.

Animals were separated from the detritus by flota­tion and were then skimmed off, the remaining water poured through a 500-|LLm sieve, and the process re­peated. Animals were preserved in 4% Formalin in sea water and later transferred to 70% ethyl alcohol.

Specimens of a second species of Nebalia were col­lected from a mud flat at Argyle Bay, Friday Harbor. San Juan Island, Washington, U.S.A., a site closer to Clark's (1932) collecting locality for N. pugettensis. These specimens were collected with a 7.62-cm di­ameter push core and then sieved on a 500-|xm .screen. Leptostracans were found in samples associated with 3 patches of decaying wood and patches of the green alga Ulva.

Written descriptions and illustrations are of the ma­ture females, as recommended by Dahl (1985), and follow the guidelines and terminology provided by him for leptostracan .systematics. However, because we are employing scanning electron microscopy (SEM), we

have added additional descriptive comments that may or may not prove to be of taxonomic importance once similar structures in other leptostracans become known. In addition, the second antenna of the male is described because of its potential importance as a tax­onomic character. Illustrations were made with the aid of a Wild M5APO dissecting microscope and a Nikon Labophot, both equipped with a camera lucida. Spec­imens subjected to scanning electron microscopy were gradually dehydrated to 100% ethanol and transferred to hexamethyldisilazane (HMDS) for air drying (see Nation, 1983). Slight sonication was used on some samples to clean the cuticular surface. Specimens to be .sonicated were rehydrated to distilled water and subjected to brief (5-10-s) bursts in an ultrasonic cleaner with low amounts of a commercial surfactant added for cleaning; these specimens then underwent ethanol dehydration and HMDS drying. After being mounted on stubs, specimens were sputter-coated with gold and examined using a Cambridge Stereoscan 360 at 1 OkV. Length measurements were made from the tip of the rostrum to the center of the posterior emargi-nation of the carapace (for carapace length) or to the tip of the caudal furca but excluding the setation (for total length). The female holotype, male allotype, 40 designated female paratypes, and many other (nonpar-atypic) specimens of the new species are deposited in the Crustacea collections of the Natural History Mu­seum of Los Angeles County (LACM). Additional paratypes have been deposited in the National Museum of Natural History, Washington, B.C. (USNM), the California Academy of Sciences, San Francisco (CAS), and the Scripps Institution of Oceanography collection (SIO).

Cursory observations of feeding behavior were made in the laboratory. To keep animals within the focal range of a vertically and horizontally tracking side-mounted dissecting microscope, narrow aquaria (30 X 30 X 3 cm) were constructed. This arrangement allowed individuals to be followed for extended peri­ods of time over the entire volume of the aquarium.

To determine whether the new species has a greater tolerance to low oxygen and elevated hydrogen sulfide relative to other animals from the same or nearby hab­itats, a preliminary and somewhat crude experiment was conducted. The new species, the amphipod Or-chomene !imode.<! Meador and Present, 1985 (also from the detrital mats), and several other species from the mats and from the adjacent sandy plain environment were placed individually in 300-ml flasks of anoxic sea water with either 1.23 mmol or 2.08 mmol of hydrogen sulfide. Virtually all oxygen was removed from the sea water by bubbling nitrogen gas through it for 30 min (verified with an oxygen meter), after which time the animals were introduced and the container was sealed while small nitrogen bubbles were still present in the water. The flasks were then maintained in a constant 18°C water bath, and the condition of the animals was checked every 30 min.

Systematics

Nebalia pugettensis (Clark, 1932) This species was originally described as

a new species of a new genus, Epinebalia,

MAETIN ET AL.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 349

by Clark (1932). The original description is vague, not only as to the collecting locality (given only as "from Puget Sound"), but also as to the features that would differen­tiate this species from others in the genus (e.g., see Dahl, 1985). There were few il­lustrations provided (2 plates) other than micrographs, which were of rather low res­olution. Furthermore, and most unfortunate­ly, we have been unable to locate any type specimens in searching the following insti­tutions: The Natural History Museum of Los Angeles County, the California Acad­emy of Sciences, the Canadian Museum of Nature, the U.S. National Museum of Nat­ural History, the Royal British Columbia Museum, the invertebrate teaching collec­tions at Friday Harbor Laboratory, Friday Harbor, Washington, U.S.A., and the Red-path Museum of McGill University in Mon­treal, Canada (where Clark was employed at the time the description was published). Regrettably, because this is a post-1930 de­scription that fails to conform to Article 13 of the International Code of Zoological No­menclature (ICZN, 1985), we are forced to declare Nebalia pugettensis (Clark, 1932) a nomen nudum (see ICZN, 1985: 260).

Nebalia hessleri, new species

(Figs. 1-13, 16) Material Examined.—Holotype 9, l,ACM 92-169.1,

carapace length (CL) 5.1 mm, total length (TL) 10.1 mm, collected 29 February 1992, Scripps Canyon, La Jolla, California, 19 m depth (see Materials and Meth­ods). Paratype 9 9, same collection data, LACM 92-169.3 (40 specimens), USNM 2g0090 (10 specimens). CASSIZ 104580 (10 specimens), SIO C 9812 (10 specimens). Allotype 8, same collection data, LACM 92-169.2. Selected other specimens destroyed in the course of dissecting for illustrations and/or SEM prep­aration.

Diagnosis of Mature Female.—Total length (excluding setation) up to 15 mm, average total length (of a series of A' = 20 of the largest individuals) 9.8 mm (total length measurements difficult to make because of strong upward curvature of abdomen); car­apace length (CL) up to 6.8 mm. Eye nor­mal (not lobed or subdivided), oval, widest in center, slightly downturned and slightly laterally compressed; pigmentation exten­sive, covering approximately distal two-thirds of eye. Antennular flagellum well de­veloped, with 14 or more segments. Dor­sum of fourth pleonite with posterior border

bearing acute teeth; tooth of posterolateral border of pleonite (the epimeron, following terminology in Dahl, 1985) slightly longer than others and slightly upturned. Base (proximal podomere or peduncle) of cor­responding limb (pleopod 4) minutely ser­rulate along posterior border, terminating in sharp tooth at posterolateral corner. Fifth pleopod with 6 large spines on distolateral border, with last spine slightly longer than others and located terminally (directed pos­teriorly). Sixth pleopod also with 6 spines along distolateral border, with sixth located terminally but much longer than (nearly twice as long as) any other spine. Rostrum with ventral projection or "keel" more or less rectangular, unpaired, but with slight medial depression gently sloping upward toward ventral surface of rostrum and with slightly protruding anterolateral corners. Caudal furcae approximately twice length of telson and sometimes greater than twice its length. Acute spines along posterior dor­sal borders of pleonites.

Description of Mature Female.—Carapace (Figs. 1, 2a): Approximately 1.5 times lon­ger than deep, unsculptured, with usual pos-terodorsal indentation.

Rostrum (Figs. 2a, b; 3b): Rostrum long, clearly extending beyond eye, distally rounded, length approximately 2.7 times width. Length of rostrum of holotype 1.5 mm. Ventral projection or "keel" more or less rectangular, unpaired, but with slight medial depression gently sloping upward toward ventral surface of rostrum and with slightly protruding blunt anterolateral cor­ners.

Compound eye (Figs. 2a, c, d; 3a, c): Large, well developed, elongate-oval and slightly downturned distally, slightly com­pressed laterally resulting in weak dorsal carina (Fig. 2d). Pigmentation (visual sur­face) extensive, covering at least distal half, with pigmented area longer than high (more or less reflecting shape of eye). Not lobed or subdivided. Base of eyestalk with minute cuticular scales visible in SEM view (Fig. 3c). Ocular (supraorbital) plate (Fig. 2c, d) sharply tapering to acute tip, relatively small, extending to approximately one-third length of eyestalk, and bearing minute setae (visible only via SEM) especially along dorsal and dorsolateral surfaces (Fig. 3c).

350 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

Fig. 1. Nebalia hessleri, new species, male (upper) and female. Note forward-curving antenna of male and eggs visible beneath cuticle in female. Photograph courtesy of Dale Stokes, Scripps Institution of Oceanography.

Antennule (Fig. 4): Peduncle composed of 4 articles. Second article widest at mid­point, with clusters of terminal and subter-minal setae as illustrated (Fig. 4a) and with single dorsal plumose seta. Third article shorter than second, widest distally, with dorsal and ventral terminal setae. Fourth ar­ticle shorter than third, with conspicuous row of 6-8 long setae and 4 (occasionally 5) stout spines, the latter increasing in size toward distal part of article, along distola-teral border; each spine bearing minute tu­bercles along curved outer surface and mi­nute subterminal pore (Fig. 4b, c). Anten-nular scale elongate and oval, extending to approximately fifth article of flagellum, bearing marginal rows of several distinct setal types (Fig. 4a, d-g), including long naked setae, stout, curved setae that are proximally smooth but distally bearing large, blunt serrations (Fig. 4e, g), and lon­ger, thinner setae bearing smaller and sharp­er teeth along their entire length (Fig. 4a, f, g). Flagellum well developed, at least 4 times length of antennular scale and com­posed of at least 14 articles, each bearing

cluster of 4 stout aesthetascs or aesthetasc-like setae and 2 thin unarmed setae at dis-todorsal border; in SEM view thinner setae curved (possibly artifact of drying) and cluster of thicker aesthetasc-like setae ap­pearing to bear minute annulations at even­ly spaced intervals (Fig. 4h).

Antenna (Fig. 5): Peduncle composed of 3 articles, proximal 2 of which with minute distodorsal teeth. Tooth of second article larger than that of first, and covered with minute teeth (visible only via SEM; Fig. 5b). Third article slightly longer than sec­ond, and bearing numerous setal types and approximately 15 stout spines (variation likely, and not documented), some of which being similar to those described for article 4 of antennule (i.e., slightly curved, bearing tubercles along outer margin, and having distal pore; Fig. 5c, d). Flagellum distinctly longer than combined articles of peduncle; each flagellar article with terminal and sub-terminal setae, most of which unarmed, and covered with minute cuticular scales (Fig. 5e, f)-

Mandible (Figs. 6a-f; 7): Palp well de-

MARTIN ETAL.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 351

Fig. 2. Nebalia hessleri, new species, holotype (a) and dissected paratype (b—h). a, Female holotype, lateral view. Scale = 1.0 mm. b. Ventral surface of rostrum showing more or less rectangular subrostral keel, c, Left eyestalk and ocular plate, lateral view, d, Same eyestalk as in (c), dorsal view, e, Posteroventral extremity of epimeron of fourth pleonite and posterior border of protopod of fourth pleopod. / Dorsolateral view of teeth along posterior border of fifth pleonite. g, Same as (/) but for sixth pleonite. h, Anal plates in ventral view.

veloped, composed of 3 articles; third arti­cle equal to or slightly longer than second; second approximately twice as long as first and with single seta at approximately four-fifths length. Setation of distal article com­

plex, with featherlike setae (i.e., with sinu­ous shaft bearing small lanceolate setules, each of which with lateral serrations; Figs. 6a, 7c, d) extending from proximal fifth to terminus, and with distal row of stouter se-

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Fig. 3. Nebalia hessleri, new species, female, selected SEM photographs of taxonomically important features. a. Anterior region showing general shape of rostrum and eyestalk. Scale = 500 |xm. al = antennule, a2 = antenna, c = carapace, e = eye, r = rostrum, s = antennular scale, b, Subrostral keel, ventral view, with anterior toward right of figure. Scale = 100 |xm. c, Anterior region of ocular plates, showing covering of minute setae. Note also the scalloped pattern of cuticular scales on the eyestalks. Scale = 100 |xm. d. Posterior region, carapace removed, showing pleonites 2-7, telson and base of caudal furca, and pleopods. Scale = 1.0 mm. e. Ventral end of epimeron of fourth pleonite and posterior border of fourth pleopod showing acute dentition. Scale = 200 |xm. / Posterior border of sixth pleonite. Scale = 100 |xm.

Fig. 4. Nebalia hessleri, new species, female, first antenna, lateral view, a. Entire appendage, right side, lateral view, b. Armature of distal end of fourth article and base of antennular scale (toward right of photograph). Scale = 100 |xm. c. Higher magnification of distal region of single spine denoted by arrow in (i>). Note tubercles and

MARTIN ET AL: NEW NEBALIA FROM SOUTHERN CALIFORNIA 353

small subterminal pore (white arrow). Scale = 10 jjim. d. Dorsolateral view of antennular scale. Scale = 100 |jLm. e. Higher magnification of stout, upturned serrate setae along dorsal surface of antennular scale border, e.g., as in boxed area of {d). Note row of longer, thinner setae arising beneath this row. Scale = 20 jjim. / Tips of several stout, serrate setae (toward left) and thinner setae of antennular scale (just distal to view in (e)). Scale = 20 |jLm. g, Higher magnification of boxed area in (/), showing armature of stout serrate setae (at top) and comblike teeth of thinner, longer setae (bottom of figure). Scale = 10 jjim. h, Setation of distal segments (3 visible in this photograph) of antennal flagellum. Note curved setae at base of each cluster of stout setae, each of which is subdivided into 3 or 4 regions by slight creases in shaft cuticle. Scale = 100 jjim.

354 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

Fig. 5. Nebalia hessleri, new species, female, second antenna, lateral view, a. Entire appendage, right side, b, Dorsal distal spine on second article of peduncle. Scale = 20 jjim. c, Setation and spination along anterior border of third article (oriented in opposite direction from drawing). Scale = 100 (xm. d. Tip of isolated spine of the type indicated by arrow in (c). Scale = 5.0 ixm. e, Several articles or "pseudoarticles" (because of incomplete sutures) of flagellum showing arrangement of setae. Scale = 100 jJim./ More distal region of flagellum showing setation and minute tubercles covering article. Scale = 50 jjim.

MARTIN ETAL: NEW NEBALIA FROM SOUTHERN CALIFORNIA 355

Fig. 6. Nebalia hessleri, new species, female, mandible, a, Entire appendage, right side, b, Distal extremity of palp showing long "sweeping" setae and more distal cluster of stout serrate setae. Scale = 50 jjim. c, Higher magnification of stout serrate setae. Scale = 20 jjim. d. Incisor process, lateral view. Scale = 50 jjim. e, Higher magnification of "comb row" of lower, sinuous blade of incisor process. Scale = 20 jjim. f, Molar process, distal end-on view (incisor process to the right). Scale = 50 jjim. g, Tracing of photograph of mandibular palp of N. pugettensis in Clark (1932) shown for comparison; differences between this and Fig. 6a are mostly because of orientation of the appendage; see text.

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Fig. 7. Nebalia hessleri, new species, female, selected SEM photographs of mandible, a. Posterior surface of distal region of palp, showing extension of row of stout, serrate setae. Note curvature of each seta at approxi­mately one-third distance from base. Scale = 1 0 0 |xm. b, Tips of stout serrate setae in box in (a) showing distal "twist" and rectangular nature of lateral setules. Scale = 20 |xm. c, Feathery sweeping setae found along upper half of palp. Scale = 50 |xm. d. Higher magnification of sweeping setae showing serrated, lanceolate setules. Scale = 20 (jim. e, f. Details of grinding surface of molar process. Scale = 5 |xm for (e), 10 |xm for (/).

Fig. 8. Nebalia hessleri, new species, female, first and second maxillae, a. First maxilla, left side, lateral view, with several setal types found on dorsal endite illustrated below, b, SEM of tridentate setae characteristic of dorsal endite, with white arrow indicating centrally located pore. Scale = 1 0 |xm. c. Long "grooming" setae of elongate palp. Scale = 20 (jim. d. Second maxilla, right side, lateral view.

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tae overlying this row. Distal stout setae curved and bearing heavy almost rectan­gular serrulations, appearing as unit to be effective scraping device (Figs. 6a-c; 7a, b). Incisor process (Fig. 6d, e) long and thin, with short sharp teeth along inner (me­dial) face. Molar process (Figs. 6a, f; 7e, f) slightly concave, with inner field composed of rows of stout, densely spaced teeth, giv­ing rise to more widely spaced teeth and long spines toward periphery.

First maxilla (Fig. 8a-c): Distal endite twice as long as proximal and carrying row of stout, distally widened and trifid setae on outer margin. Other setal types including long setose or simple setae restricted to dis­tal part of endite, and row of spatulate setae just distal to row of trifid setae (Fig. 8a). Trifid setae nearly smooth basally, giving rise to smooth setules toward distal tip, and with central of 3 terminal teeth slightly lon­ger than flanking teeth and bearing small pore (white arrow. Fig. 8b). Palp approxi­mately 5 times longer than combined length of both endites of protopod and bearing evenly spaced, long setae, each appearing naked under light microscopy, but bearing minute lateral setulations visible under SEM; each seta strongly recurved and bear­ing longer setules at extremity (Fig. 8c)

Second maxilla (Fig. 8d); Protopod sub­divided into 4 endites, with endites 1 and 3 approximately equal in size and larger than either endite 2 or 4. Endopod longer than exopod, composed of 2 articles, basal one longest and slightly shorter than exopod. All endites, endopod, and exopod bearing plumose setae; distal plumose setae of sec­ond article of endopod very long, approach­ing length of entire limb.

Thoracopods (Fig. 9): Endopod always exceeding length of exopod. Distal article of endopod of each thoracopod slightly en­larged, turned rather sharply at angle from main axis, and bearing numerous long, plu­mose setae (Fig. 9d-f), thereby indicating mature females (following categorization of Dahl, 1985: 140; figs. 6-10). Plumose setae of distal article of endopod extremely dense, with setules long and overlapping with those of adjacent setae on the same appendage and also with those of opposing (opposite side) thoracopod, forming floor of brood pouch (Fig. 9e, f). Endopod weakly divided into articles, sometimes appearing

to have 1, other times 2 or 3, suture lines separating distal articles. Exopod extending to approximately 0.8 to 0.9 length of en­dopod, unarmed or with scattered simple setae along margin, distally widest, always exceeding length of epipod. Epipod more or less bilobed, with lobes divided by thin band of presumed connective tissue; epipod becoming less obviously bilobed and de­creasing in size relative to endopod in pos­terior limbs (e.g., compare thoracopods 1 and 4 (Fig. 9a, b) with thoracopod 8 (Fig. 9c)).

Pleonites: Posterior borders of all pleon-ites bearing sharp, widely spaced teeth (Figs. 2a, f, g; 3f) and with slightly scal­loped cuticular scales bearing minute teeth along posterior border (visible only under SEM; Fig. 3f).

Fleopods 1 ^ : First pleopod (Fig. lOa-d) exopod approximately two-thirds as long as protopod. Exopod with approximately 36 stout, serrate spines along lateral border (Fig. 10b, d), 4 stout smooth spines on dis-tolateral border increasing in size toward apex, with terminal spine by far largest, and approximately 20 plumose natatory setae along medial margin. Under SEM, stout serrate spines of the lateral border distally tridentate, with stout central projection flanked on either side by sinuous, acutely tipped shorter projection. Endopod slightly longer than exopod, 2-segmented, with plu­mose setae on lateral and medial borders of distal (longer) segment and with basal seg­ment giving rise to short appendix interna. Appendix interna bearing 3 short, stout, dis­tally recurved hooks (retinacula) for cou­pling with similar hooks on appendix inter­na of opposing first pleopod of other side. Protopod with stout, smooth spines arising near base of endopod and exopod as shown (Fig. lOa-c). Second pleopod (Figs. lOe, 11) exopod without row of stout serrate se­tae, instead with row of spine pairs; spine pair consisting of 1 long and 1 short spine, both covered with minute triangular cutic­ular scales on all but tip, and both with sub-terminal, twisted seta of presumed sensory function (Fig. l i e , d). Endopod with long natatory setae on lateral and medial bor­ders. Both endopod and exopod with long heavy spine at distal terminus. Appendix in­terna with 3 stout recurved hooks (retinac­ula, Fig. l l f) as described for pleopod 1;

MARTIN ET AL.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 359

/ / Fig. 9. Nebalia hessleri, new species, female, selected thoracopods. a, Thoracopod 1, left side, anterior view. b, Thoracopod 4, right side, anterior view, c, Thoracopod 8, right side, anterior view, d, Thoracopod 7 (different animal) to show approximate setation. e, Detail of tip of endopod of same thoracopod shown in {d) to illustrate density of setules. / SEM of same region. Scale = 200 ixm.

these hooks protected ventrally by setose papillae extending ventrally and medially to cover them, not visible in ventral view with opposing pleopods (right and left) coupled (Fig. l ie) . Protopod with long, stout spines near bases of endopod and exopod, and with row of sabrelike teeth on anterolateral corner (Figs. 10b, 1 la, b). Third and fourth pleopods presumed similar to second, not

examined in detail (see Figs. 2a, 3d for low magnification views).

Pleopods 5 and 6: Pleopod 5 (Fig. 12a-c) 2-segmented, uniramous, with 6 well-de­veloped spines along distal lateral and ter­minal border, increasing in size distally, and with numerous setae lining medial border; these long setae on medial border being somewhat "jointed" at approximately mid-

360 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

Fig. 10. Nebalia hessleri, new species, female, first and second pleopods. a. First pleopod, left side, anterior view, b, SEM photograph of pleopods 1—3 (partial) in situ. Note row of stout tridentate spines along lateral border of exopod of pleopod 1. Scale = 200 |xm. c, SEM photograph of pleopod 1, anterior view showing basal region of endopod and exopod and appendix interna. Scale = 200 |xm. d, SEM photograph of characteristic stout serrate setae from lateral border of exopod, pleopod 1. Scale = 20 |xm. e, pleopod 2, left side, anterior view, and part of appendix interna of opposite side (pleopod 2, right side).

MARTIN ETAL.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 361

Fig. 11. Nebalia hessleri, new species, female, SEM photographs of pleopods 1 and 2. a, Pleopod 2, distal region of protopod and base of exopod, and pleopod I, comb row of stout serrate setae (at lower left). Note knifelike serrations of anterolateral corner of pleopod 2 protopod (white box) where it contacts comb row of pleopod 1. Scale = 100 |xm. b, Higher magnification of knife-like serrations indicated in (a). Scale = 5.0 |xm. c. Pairs of stout spinelike setae, lateral border of exopod of pleopod 2. Scale = 50 |xm. d. Detail of tip of spinelike seta indicated by box in (c). Note covering of triangular scales directed distally, smooth terminus, and twisted subterminal seta. Scale = 10 |xm. e, Appendix interna of pleopod 2 (right and left sides coupled), ventral view, showing setose fleshy papillae covering interlocking coupling hooks (retinacula). Scale = 50 |xm. / Appendix interna, pleopod 2, hooklike coupling setae (uncoupled from corresponding pleopod). Scale = 20 |xm.

length; there corrugations of cuticle appear­ing to confer some flexibility on setal shaft (Fig. 12b, c). Pleopod 6 1-segmented, uni-ramous, with 6 lateral and distal spines in­creasing in size distally and with scattered simple setae among these spines and along medial border. Terminus of pleopod at ori­

gin of distalmost spine bearing circlet of sharp teeth (Fig. 12f). Lateral and distal spines of both pleopods 5 and 6 covered with short triangular scales and bearing short, twisted subterminal seta of presumed sensory function (Fig. 12g). Both pleopod pairs with broad triangular ventral process

362 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

Fig. 12. Nebalia hessleri, new species, female, pleopods 5 and 6. a, Pleopod 5, right and left, ventral view, b, SEM photograph of right pleopod 5, ventral view. Scale = 200 \x,m. c. Higher magnification of box shown in (b), showing annulations presumed to confer flexibility on setal shaft. Scale = 5.0 jjim. d, Pleopod 6, left side, ventral view, e, SEM photograph of right and left pleopod 6, ventral view. Scale = 200 jjim. f, Higher magni­fication of box shown in (e), showing circlet of sharp teeth surrounding base of distalmost spine of pleopod. Note also cuticular microscales. Scale = 20 jjim. g, Tip of penultimate spine, indicated by box in (e). Note covering of triangular scales, terminal area lacking scales, and twisted subterminal seta, as described for anterior pleopods (Fig. l id) . Scale = 5.0 \Lm.

extending posteriorly between bases of rami, more acutely triangular and longer in pleopod 6 (Fig. 12a, d, e).

Telson, anal plates, and caudal furca: Tel-son (Figs. 2a, 3d, 13a, b) short, approxi­mately as long as wide, rectangular, or with sides slightly diverging posteriorly. Anal plates (Figs. 2h, 13c) sharply tapering from

broad base to acute extremity, with outer (lateral) borders smoothly curved and with medial borders slightly bulging along mid-length; overall appearance more acute than typical for genus. Caudal furca elongate, ranging from slightly less than 2 times to more than 2.3 times length of telson, ap­proximately equal to length of telson plus

MARTIN ETAL: NEW NEBALIA FROM SOUTHERN CALIFORNIA 363

Fig. 13. Nebalia hessleri, new species, female, telson, anal plates, and caudal rami, a, Telson and caudal rami, ventral view, b, SEM photograph of same region. Suture line connecting telson with anterior somite occurs just at upper edge of photograph. Scale = 1.0 mm. c, Anal plates (upper box in {b)), ventral view. Scale = 1 0 0 |xm. d, Lateral spines of caudal ramus (lower box in {b)). Note covering of minute microscales. Scale = 50 |xm.

pleon segment 7. Furcal rami each with 16-20 spines along inner margin and with up to 24 spines along lateral margin; these spines gradually increasing in length pos­teriorly with last two much longer than any of anterior spines; of these last two spines terminal being longer, almost twice length of penultimate spine. Inner margins of each branch also bearing short setae.

Coloration: In life, specimens appeared mostly transparent except for bright red

eyes. When viewed with naked eye thoracic region appearing almost white. Some males with slightly ruddy hue, especially in tho­racic region. Eggs (barely visible in Fig. 1, lower photograph) are gold or cream col­ored.

Distribution.—To date known only from the type locality. Our prediction is that the known range will increase with heightened efforts at collecting and identifying leptos-

364 JOURNAL OF CRUSTACEAN BIOLOGY. VOL. 16. NO. 2. 1996

tracans throughout California and other lo­calities in the eastern Pacific.

Etymology.—We are pleased to name this species after our friend and colleague, Rob­ert R. Hessler, in honor of his many excel­lent contributions to crustacean morphology and systematics.

Remarks.—The new species shares some features with specimens collected from Fri­day Harbor, Washington. These characters include common eye morphology, with both species possessing "normal" leptos-tracan eyes, and the shape of the male sec­ond antenna. It can be differentiated from that species by the shape of the teeth along the posterior borders of the pleonites, the shape and dentition of the epimeron of the fourth pleonite, the relative lengths of the caudal furca and telson, and by overall size (see Discussion).

The new species differs from all other described species of Nebalia in having 14 or more segments on the antennal flagellum of mature females and a rostrum that is ap­proximately 2.7 times longer than wide (see Discussion). A smaller cooccuring species of Nebalia, occupying a different microhab-itat (adjacent sand flats), is easily distin­guished by the greatly reduced antennular flagellum and by the presence of unusual lobes on the eye of the sand-flat species (Vetter, in press).

NATURAL HISTORY

Preliminary Observations on Feeding In the laboratory, leptostracans fed on

large pieces of meat (e.g., fish, shrimp, fish-containing cat food, and squid) by scraping off chunks, using the peduncle of the first antenna, which bears a row of strong spines (e.g.. Fig. 4b). The animals remained in contact with the meat often for five minutes or more, and produced a continuous fecal strand that sometimes rivaled the length of the animal. In such cases, the fecal strand was the same color as the food and thus possibly was poorly processed. If sufficient numbers of individuals were present, they completely covered the meat, apparently using their antennules both to brace them­selves against the food and to hold on to it. With tough pieces of meat, such as squid, N. hessleri tore off a piece of meat and laid on its back while processing it with its

mouthparts. The meat was rapidly tumbled and turned in front of the mouth until it was either entirely consumed or was ejected by a current of water that shot out from the region of the mouth in a line normal to the long axis of the animal. When large pieces of food were not present, the animals fed by lying on their backs and using their an­tennules to cast sediment into the space be­tween their thoracopods. This material was then moved toward the mouth and tumbled around the mouthparts. Some particles were rejected immediately via the stream of wa­ter flowing out from the mouth region, whereas other particles were tumbled for variable periods before being ejected. Ani­mals fed only field-collected, organically enriched sediments grew and reproduced normally. Within the detritus mat habitat of these animals, vertebrate and invertebrate carcasses are frequently seen and are ex­ploited by A . hessleri and the lysianassoid amphipod Orchomene limades Meador and Present, 1985, which is also extremely abundant in this habitat (Vetter, 1994). In­deed, these two species, A . hessleri and O. limodes, are the dominant crustaceans in this rich habitat and are the primary con­tributors to what is now known as the high­est density of any macrofaunal assemblage yet reported, with an estimated 2 million individuals/m^ (Vetter, 1994). Cannibalism was observed on several occasions. When live, but apparently distressed, adults (a slightly opaque white, rather than clear, ap­pearance was taken to indicate some type of distress) were attacked, the aggressor in­serted its head into the victim's thoracic cavity and, apparently with some difficulty, partially ate the victim's thoracopods. Once the victim was dead, the back of the head was also eaten. When dead conspecifics were provided, N. hessleri similarly con­sumed the thoracopods and the head.

Preliminary Observations on Oxygen Level Tolerance

Nebalia hessleri lives in thick detritus mats with low oxygen levels (Vetter, 1995) and, judging by the odor, elevated sulfide. In the laboratory, when not swimming or burrowing, the animals typically rested on their backs or sides. The thoracic append­ages rarely stopped moving. Occasionally, when the animals were neither swimming

MARTIN iiJ .4L.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 365

nor feeding, the thoracopods would be mo­tionless, but rarely for more than a few min­utes. When placed in anoxic or hypoxic wa­ter, the animals swam to the surface and rested on the side of the aquarium with their heads in the surface film, using their thor­acopods to draw water from the very sur­face of the aquarium over their respiratory appendages. Placed in a stoppered flask of anoxic water, they behaved normally for 8-12 h, after which they sought out the sur­face. With no air-water interface available they eventually settled to the bottom and continued to beat their thoracopods. They then occasionally swam to the top of the flask and then swam around the flask, pre­sumably searching for more favorable con­ditions. Most animals perished after 14 h in anoxic conditions (Vetter, 1995), but re­vived completely if removed to aerated wa­ter just prior to death (i.e., at around 13 h).

When exposed to both anoxic conditions and high sulfide levels, animals behaved similarly but died sooner (6-7 h; Fig. 15). The results were roughly similar for the am-phipod Orchomene Umodes, which occurs with N. hessleri in the detrital mats. Sur­vival for both N. hessleri and O. Umodes was far greater than it was for another am-phipod (Aorides spinosus Conlan and Bous-field, 1982) that occurs in both the detritus mats and the adjacent sand flat. As might be expected, crustaceans and one pycno-gonid known only from the relatively well-oxygenated sand-flat area died relatively quickly under these conditions (Fig. 15).

DISCUSSION

Comparison to Other Descriptions of Leptostracans from the West Coast of

North America

One of the factors hindering leptostracan taxonomy along the west coast of North America has been the rather incomplete original description of Nebalia pugettensis (as Epinebalia) by Clark (1932). Clark il­lustrated few of what are now considered taxonomically important features of leptos­tracans (see Dahl, 1985), and unfortunately did not deposit any type material, according to our search of United States and Canadian natural history museums. Without type ma­terial or a detailed description for compar­ison, subsequent workers have had to as­

sume that any Nebalia encountered on the west coast must belong to that species, and thus virtually all guidebooks and keys (e.g., Reish, 1972; Haderiie et at. 1980; Rickets et al, 1985; Smith and Cariton, 1980; Ko-zloff, 1987) list this species as the sole west coast representative of the Nebaliacea (al­though Kozloff, 1987: 320, was aware of an undescribed species in the intertidal and subtidal of the Pacific Northwest). Because of this uncertainty, we were forced to de­clare N. pugettensis a nomen nudum.

We have examined specimens from Fri­day Harbor, Washington, a site much closer to the original collecting site for N. puget­tensis (Puget Sound, Washington) than is our collecting site off La Jolla, California. There is no guarantee that these specimens belong to the species described by Clark, since there may be several species found in that area. We point out here the following features (some of which are shown in Fig. 14) that serve to differentiate between these Friday Harbor specimens and N. hessleri. (1) In the Friday Harbor specimens the epi-meron of the fourth pleonite bears shorter, broader, and blunter teeth along its posterior border, and the posterolateral comer tapers more gradually toward a blunt tip (Fig. 14a). The basal article of the corresponding fourth pleopod does not bear sharp teeth along its posterior border (compare Figs. 14a, 2e, 3e). (2) The posterior borders of pleonites 5 and 6 (Fig. 14b), and indeed of all pleonites, bear short, closely spaced teeth that are markedly truncated distally, appearing nearly rectangular, in the Friday Harbor specimens (Fig. 14c). (3) The cau­dal furcae in the Friday Harbor specimens are relatively short, exceeding the length of the telson, but clearly less than twice its length (Fig. 14d), whereas in A . hessleri the caudal furcae are sometimes more than twice the length of the telson (Fig. 13a, b). (4) Overall differs significantly, with

the new species attaining lengths of up to 15 mm in adult females (although 9-11 mm is more common), versus 7 mm in our Fri­day Harbor specimens and reported by Clark (1932: 226) for N. pugettensis. Dahl (1985: 136) also described specimens of Nebalia from this area (which he referred to as N. pugettensis) as small, with "cara­pace lengths only rarely exceeding 3.5 mm" (versus up to 6.8 mm in N. hessleri).

366 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

Fig. 14. Selected features of specimens (female) of an undescribed species of Nebalia collected at Friday Harbor, Washington, a. Posterolateral border of fourth pleon and base of corresponding limb (fourth pleopod). Note size and shape of teeth as compared to Fig. \e, 2e. Scale = 200 jjim. b, Dorsolateral region of pleon 5 and 6. Scale = 100 jjim. c, Higher magnification of teeth along posterior border of pleon 6. Note truncate terminus as compared to similar teeth in Figs. 1/ g, 2 / Scale = 50 jjim. d. Ventral view of telson, anal plates, and caudal furca. Compare relative size of furcal rami to telson with what is seen in Figs, la, 12a, b. Scale = 500 jjim.

(5) In addition, although not shown here, the coloration of the eggs may differ be­tween these species. In N. hessleri, eggs are cream or gold colored, whereas eggs are ap­parently pink in at least one species of Ne­balia from Moss Landing, California (per­sonal communication, Cathy LeFaye, Moss Landing, California). In light of our declar­ing N. pugettensis a nomen nudum and the uncertainty of identifications of west coast leptostracans, there is at this time no cer­tainty as to the identity of the Moss Land­ing species. Those specimens came from a similar intertidal mud-flat habitat as did our Friday Harbor specimens.

Although the figure of the mandibular palp of N. pugettensis in Clark (1932) is very different from that in the present study (Figs. 6a-f, 7), this should not be consid­ered a diagnostic character. Clark's figure (reproduced here as Fig. 6g for comparison)

is a photograph taken from a posterior an­gle, in such a way that the palp is oriented with its flat blade parallel to the body axis. In other words, the distal article was pho­tographed on edge, resulting in the thin, elongate appearance seen in Fig. 6g (traced from Clark's photograph). The curving, "rasping" setae described by Clark (1932) are part of the row of curved stout setae on the external (outer) face of the distal article of the palp (Figs. 6b, c, 7a, b); turning the mandible of N. hessleri on edge yields a profile similar to that shown by Clark.

Dahl (1985), in his revision of the Eu­ropean shelf species of Nebalia, included some valuable ontogenetic data for reared specimens of what he called A . pugettensis (see Dahl, 1985: 137, table 1). His speci­mens came from "near the Marine Biolog­ical Station at Friday Harbor, Washington," and were apparently from a mud environ-

MARTIN ET At.: NEW NEBALIA FROM SOUTHERN CALIFORNIA 367

GOOD

OX)

Fig. 15. Comparison of survival time (in hours) un­der conditions of anoxia and elevated sulfide levels for arthropod species known only from the detrital mats {Nebalia hessleri, Orchomene limodes) versus a spe­cies that occupies both the detrital mats and adjacent, better oxygenated sand flats (Aoroides spinosus) versus several species known only from sand flats. L = lep-tostracan, A = amphipod, I = isopod, T = tanaida-cean. Circles represent higher concentrations (2.08 mmol) of hydrogen sulfide.

ment, since he stated that "sifted mud from the collecting site" was pipetted into the dishes from time to time to renew their food supply (Dahl, 1985: 136). Thus, our Friday Harbor specimens (Fig. 14) and Dahl's specimens may belong to the same species, although there is also the strong likelihood that such areas contain more than one spe­cies of leptostracan, as we are finding to be the case in southern California. The habitat of Clark's specimens was not listed by her; she stated only that they came "from Puget Sound" via the Pacific Biological Labora­tories in Pacific Grove, California. Packard (1883) mentioned a species that he felt was similar to the European A . bipes (O. Fabri-cius, 1780) collected from "just below low-water mark among fucoids" (as cited by Clark, 1932: 225; Packard's monograph not seen by us). Our specimens were collected from a mudflat, as apparently were those of Dahl (1985). Packard also mentioned hav­ing collected "what is probably a fifth spe­cies" between tide marks at Victoria, Van­couver Island, British Columbia. According to Clark (1932), that specimen was lost. This lost specimen might be what Kozloff (1987: 320) was referring to when he men­tioned an undescribed species in the Pacific Northwest. Thus, whereas there is little

doubt that the two species described in our paper are distinct, there are almost certainly other undescribed species along the Pacific Northwest, and there is no guarantee that our Friday Harbor, Washington, specimens are the same as, or even morphologically close to, whatever Clark (1932) described as A . pugettensis.

Comparison to Other Species of Nebalia Leach, 1814

The possibility that A . hessleri is an in­troduced species was considered in light of the increasing problem of exotic species be­ing introduced into California via shipping (e.g., see Carlton and Geller, 1993). How­ever, several features serve to separate N. hessleri from any other previously de­scribed member of the genus. First, the an-tennular flagellum of the mature female bears 14 or more segments (Figs. 2a, 4a). No other species is known to have more than 11; this number of segments is seen only in females of A . falklandensis Dahl, 1990, A . antarctica Dahl, 1990, A . strausi Risso, 1826, A . herbstii Leach, 1814, and the male of the species that occupies sand flats adjacent to the habitat of A . hessleri (Vetter, in press). In addition, the rostrum of A . hessleri is approximately 2.7 times its width. Nebalia longicornis Thomson, 1879, and the undescribed sand-flat Nebalia have long, thin rostrums as well, but neither ex­ceeds a length of 2.6 times the width. This combination of features distinguishes A . hessleri from all other species in the genus.

Note on Males of A . hessleri

Because of the rarity of males in most populations (and therefore in most collec­tions) of leptostracans, Dahl (1985) rec­ommended that they not be used in species descriptions. However, males in our collec­tions are relatively common. Although not counted, we estimate that males constituted perhaps 20% to 40% of our collections. Ad­ditionally, we found it interesting that, al­though there can be little doubt as to the distinctness of our new species, males of A . hessleri are similar to males of Clark's (1932) ''Nebalia pugettensis,'" in at least one character. Males of A . hessleri have a second antenna that is curved rather sharply in an anterior direction. Most often this condition appears as in the male allotype of

368 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO. 2, 1996

N. hessleri (Fig. 16a), but considerable vari­ation exists, with the antenna sometimes ex­tending almost directly anteriorly (Fig. 16b) and at other times curved medially so that the two opposing rami are crossed (Fig. 16c) or even appearing slightly cork­screwed (Fig. 16d). Clark (1932: 225) de­scribed this as "forwardly directed, sickle-shaped antennae, bearing a strong resem­blance to the antennules of male cyclo-poids ," and based her new genus Epinebalia on this one character of the males.

Functional Morphology

Another factor that currently hinders comparisons of N. hessleri with other spe­cies of Nehalia along the west coast is that very few species have been examined via SEM. Thus, it is difficult to know whether some of the unusual ultrastructural features described herein, such as the twisted distal subterminal seta on the pleopodal spines, or the minute pore on the tip of the spines found on the antennular fourth article, are unique to this species versus shared by some or all members of the genus or per­haps shared by all leptostracans. The only previous electron microscope studies of lep­tostracans of which we are aware are the survey of European shelf species by Dahl (1985), which included only two SEM plates, a brief note on epipods by ltd (1988), and the study of spermiogenesis (coincidentally also using 'W. pugetten-sis") by Jesperson (1979), in which only transmission electron microscopy was em­ployed. Dahl's SEM photographs included only the dorsolateral teeth of the sixth and seventh pleonite borders in four species (his figs. 107-114) and one view of the setae of the first pleopod of N. horealis (his fig. 115). The acutely toothed pleonite borders of N. hessleri (Figs. 2f, g, 3f) are most sim­ilar to those of M horealis (see Dahl, 1985: figs. 109, 110). The rich diversity of spine and setal types and the cuticular scales sug­gest that SEM may prove to be a valuable tool in leptostracan systematics, as has cer­tainly been the case for other small crusta­cean taxa.

Some of the features illustrated herein are possibly indicative of sensory roles. This is true for the spines of the fourth article of the antennule, which bear a pore on the dis­

tal outer surface (Fig. 4b, c). A similar con­dition is seen in the spines bordering the distal article of the antennal peduncle (Fig. 5a, c, d). Although it is certainly possible for setae and spines lacking such pores to be chemosensory devices, with chemical mediators being transported across the thin cuticle of the appendage instead of via a pore (Laverack and Barrientos, 1985), it is unlikely that such pores would be present on a seta or spine with no such function. An alternative explanation, that these de­pressions are "molting pores," is easily dis­missed by comparing the presumed chemo­sensory setae to surrounding spines and se­tae, none of which bear a similar terminal depression. Pores are also seen on the cen­tral spike of the tridentate spines of the first maxilla (Fig. 8a, b). Although these spines and setae have been illustrated accurately by previous workers (in this genus and in other leptostracan genera), the pores are a new finding, and suggest a sensory role in addition to the mechanical function of this limb. Also suggestive of a sensory function are the thin, twisted setae found on the sub-terminal undersurface of the rather heavy spines of the pleopods (Figs, l i e , d, 12e, g). Although we did not obtain sufficient resolution to determine whether these thin, straplike setae have distal openings, the im­pression given is that they do (especially see Figs. 1 Id, 12g).

Although SEM has not been widely ap­plied to leptostracans for taxonomic pur­poses, some authors have illustrated spine and setal types that appear very similar to those we have shown in N. hessleri. For example, the characteristic spines along the lateral border of the first pleopod have been illustrated in nearly all descriptions of lep­tostracan species, and the better illustrated accounts (e.g., Wagele, 1983; Hessler, 1984) even include figures of the array of setal types on the maxillae, pleopods, etc. The emerging picture is one of great uni­formity of setal and spine types in this or­der. Even in those species occupying dis­parate and unusual habitats (e.g., Dahlella at deep-sea hydrothermal vents, Speoneba-lia in caves), the setal types and their lo­cations appear similar. Despite the fact that we have revealed previously unknown ul­trastructural details of setae and spines in one leptostracan, overall it appears that di-

MARTIN ET AL: NEW NEBALIA FROM SOUTHERN CALIFORNIA 369

Fig. 16. Nebalia hessleri, new species, figures of the male second antenna, a. Allotype male, CL 2.8 mm excluding rostrum, same collection data as for female types, with first and second antenna illustrated, b-d. Variations in the shape and curvature of the flagellum of the second antenna (both right and left sides shown in (c) and {d)) in similar-sized males in the collection.

370 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 16, NO, 2, 1996

versity of these structures within the Lep-tostraca is not great. Thus, although ultra-structural details may provide species-spe­cific characters, we are in agreement with Dahl's (1985: 138) statement that among leplostracan species and genera "basic ar­mature pattern is remarkably uniform." This also leads us to suspect that structures newly described here as being sensory in nature, such as the subterminal twisted seta on the pleopodal spines, are probably to be found in other leptostracans as well.

Finally, this work supports and under­scores the comments of Dahl (1987) con­cerning the morphology of leptostracans as compared to other "phyllopodous" crusta­ceans (particularly the Branchiopoda). The SEM photographs highlight the fact that even at an ultrastructural level, the thora-copodal appendages of nebaliaceans are grossly different from those of branchio-pods, possessing a suite of spines and setae such as is seen in no living or extinct bran-chiopod (e.g., see Martin et ah, 1986; Mar­tin, 1992; Martin and Christiansen, in press).

Because so few SEM studies exist for other species of Nehalia or other leptostra-can genera, for purposes of identification at present we recommend reliance on previ­ously recognized morphological (versus ul­trastructural) characters, and suggest the following key to leptostracan families and genera (mostly compiled from information in Hessler, 1984; Dahl, 1985; Bowman et al, 1985; and Modlin, 1991).

KEY TO THE EXTANT FAMILIES AND GENERA OF THE L E P T O S T R A C A

I. Thoracic region appearing inflated. Carapace and body cuticle thin, membranous. Carapace lacking posterior medial indentation and with slight sculpturing. Mandible lacking incisor pro­cess and with reduced molar process. First max­illa with palp reduced to small stub. Second maxilla nearly as large as thoracopod 1; endopod 1-segmented and reduced to small, blunt, distal lobe; exopod absent; proximal endite enormous­ly enlarged. Pleopods l-A with exopods paddle­like, less than 3 times longer than wide. Caudal rami leaflike, broadest at midpoint

Family Nebaliopsidae Hessler, 1984 (Nebaliopsis G. O. Sars, 1887)

- Thoracic region not inflated. Carapace and body cuticle more or less firm. Carapace strongly emarginate (indented) posteromesially and lack­ing sculpturing. Mandible with well-developed incisor (Paranehalia is an exception to this) and

molar process. First maxilla with palp long, well developed. Second maxilla much smaller than thoracopod 1; endopod I- or 2-segmented; en­dopod and exopod well developed, each longer than wide; first three endites similarly developed (proximal endite not enormously enlarged, al­though slightly larger than other endites), Pleo­pods 2-A with exopods slender, more than 4 times longer than wide. Caudal rami tapering evenly from base to tip , , .2 (Family Nebaliidae

Baird, 1850; emend. Hessler, 1984) 2, Eyestalk long, clearly exceeding rostrum in ma­

ture individuals, gently curved or abruptly an­gled ventrally, tapering distally, lacking any vi­sual pigment 3

- Eyestalk short, not exceeding length of rostrum in mature individuals (or, if exceeding length of rostrum, then not deflected ventrally [Speane-halia]}, widest at midpoint (not tapering), with or without visual pigment 4

3, Eyestalk with abrupt angle on anterodorsal sur­face, and with anterior margin flattened and bearing minute lobes. Second maxilla with ex­opod reduced, less than half length of proximal article of endopod. Posterior emargination of carapace lacking minute spines along either side of midpoint, Thoracopods with well-developed epipods Dahlella Hessler, 1984

- Eyestalk smoothly curving on anterodorsal sur­face, banana- or sausage-shaped, not flattened on anterior margin, lacking minute lobes. Second maxilla with exopod more than half length of proximal article of endopod {usually exceeding length of proximal article of endopod). Posterior emargination of carapace minutely spinulose along either side of midpoint, Thoracopods lack­ing epipods Nebaliella Thiele, 1904

4, Pleopod I with row of stout, equally sized, com­plex serrate spines along outer (lateral) margin of exopod. Eyes with at least some visual pig­ment 6

- Pleopod 1 lacking row of stout, equally sized, complex serrate spines along outer (lateral) mar­gin of exopod. Eyes lacking visual pigment , , 5

5, Carapace long, extending posteriorly to ju.st be­yond level of fifth pleonite, sometimes as far as sixth pleonite, Eyestalks narrow, tapering distal­ly, slightly exceeding length of reduced rostrum. Maxilla 2 endopod I-segmented, with series of oval organelles (glands). Rostrum lacking distal spine. Caudal rami very short, length approxi­mately equal to width of telson, with densely spaced long setae

Speonebalia Bowman et al., 1985 - Carapace short, not extending posteriorly be­

yond fifth pleonite. Eyestalks laterally com­pressed, disc-shaped or subrectangular, never ex­ceeding length of rostrum. Maxilla 2 endopod 2-segmented, lacking glands. Rostrum with minute distal spine articulating with rostral cuticle. Cau­dal rami slender, length more than twice length of telson, with widely spaced setae

Sarsinebalia Dahl, 1985 6, Antenna 1 peduncle distal (fourth) segment with

distolateral, toothed processes, but not with ar­mature of spines (as, e,g,, in Nebalia). Mandib­ular incisor weakly developed, Thoracopods nar-

MARTIN EZAL: NEW NEBALIA FROM SOUTHERN C-JUJFORNIA 37 P

row and long, almost flagelliform. Epipods of thoracopods present but reduced in size, with surface area less than half that of endopod. Eyes often bearing spines that increase in size distally

Paranehalia Claus, 1880 - Antenna 1 peduncle distal (fourth) segment

without distolateral, toothed process, instead with stout spines. Mandibular incisor well de­veloped. Thoracopods expanded, leaflike. Epi­pods of thoracopods well developed, surface area clearly one-half or more that of endopod. Eyes sometimes with blunt lobes but never with numerous spines

Nebalia Leach, 1814

ACKNOWLEDGEMENTS

Both JWM and CCC thank EWV for originally bringing these specimens to our attention, and for dis­cussing with us some of the many interesting morpho­logical features of leptostracans. This paper resulted in part from a 1993 meeting of SCAMIT, the Southern California Association of Marine Invertebrate Taxon-omists. We thank the members of that organization for their many helpful comments and suggestions. We also thank Alicia Thompson of the University of Southern California's Center for Electron Microscopy and Mi­croanalysis for assistance with the SEM portion of the study, and Dale Stokes of the Scripps Institution of Oceanography for the photograph used as Fig. 1. Be­cause of the superficial similarity of leptostracans to some branchiopod crustaceans, this work was suggest­ed by reviewers of, and directly supported by, U.S. National Science Foundation grant number DEB-90200898 to J. W. Martin.

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RECEIVED: 10 July 1995. ACCEPTCD: 1 November 1995.

Addresses: (JWM and CEC) Natural History Mu­seum of Los Angeter County, 900 Exposition Boule­vard, Los Angeles, California 90007, U.S.A.; (EWV) Scripps Institution of Oceanography, La Jolla, Califor­nia 92093, U.S.A.